frangible \FRAN-juh-buhl\, adjective:
Capable of being broken; brittle; fragile; easily broken.
That's because Federal Aviation Administration regulations call for a "sturdy" but "frangible" -- or breakaway -- door. "It must be able to break away at the lock, the hinge or the door handle" to allow pilots to get out in emergencies, Olsen says.
-- Blake Morrison, "Flight decks vulnerable to passenger attacks", USA Today, January 5, 2001
The red-gray, meringuelike substance ices some of the cave's surfaces and ledges like cake frosting, from a millimeter to several inches thick, and is so frangible you could cut it with a butter knife.
-- Peter Nelson, "The Cave That Holds Clues To Life On Mars", National Wildlife, August/September 1996
Frangible ultimately derives from Latin frangere, "to break."